Cosmic ray energy changes at the termination shock and in the heliosheath

Voyager 1 crossed the termination shock of the solar wind in December 2004 at 94 AU and currently measures the cosmic ray intensity in the heliosheath. To better understand this modulation region beyond the shock, where adiabatic energy changes should be small, we review the net effect of energy changes during the modulation process, including adiabatic deceleration in the solar wind, acceleration at the termination shock, and the possibility that stochastic acceleration in the heliosheath may also make a contribution

Cosmic-ray energy changes in the heliosphere. II. The effect on K-capture electron secondaries

Recent accurate measurements of the cosmic-ray intensity ratio ^(51)V/^(51)Cr below 1 GeV nucleon^(-1) provide a powerful new tool to study cosmic-ray modulation in the heliosphere. This paper describes how energy changes during this modulation process influence this ratio. In particular, our model includes acceleration at the solar wind termination shock, and we find that this mechanism significantly enhances the ^(51)V/^(51)Cr ratio at 1 AU. It is also shown that this acceleration makes the ratio more sensitive to the form of local low-energy interstellar spectra, below ~100 MeV nucleon^(-1), than without it. Specifically, this acceleration provides an independent confirmation of the consensus that low-energy spectra should be flatter than their high-energy power-law forms

Depletion of chlorine into HCl ice in a protostellar core

The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances $<10^{-5}$ has not yet been well studied. Our aim here is to study the depletion of chlorine in the protostellar core, OMC-2 FIR 4. We observed transitions of HCl and H2Cl+ towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H$_{2}$ hyperfine collisional excitation rate coefficients. A narrow emission component in the HCl lines traces the extended envelope, and a broad one traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9e-11, a factor of only 0.001 that of volatile elemental chlorine. The H2Cl+ lines are detected in absorption and trace a tenuous foreground cloud, where we find no depletion of volatile chlorine. Gas-phase HCl is the tip of the chlorine iceberg in protostellar cores. Using a gas-grain chemical model, we show that the hydrogenation of atomic chlorine on grain surfaces in the dark cloud stage sequesters at least 90% of the volatile chlorine into HCl ice, where it remains in the protostellar stage. About 10% of chlorine is in gaseous atomic form. Gas-phase HCl is a minor, but diagnostically key reservoir, with an abundance of <1e-10 in most of the protostellar core. We find the 35Cl/37Cl ratio in OMC-2 FIR 4 to be 3.2\pm0.1, consistent with the solar system value.Comment: 13 pages, 12 figures, accepted for publication in A&

The effect of cosmic ray energy changes in the heliosphere on K-capture

In an accompanying paper we give a re-assessment of cosmic ray energy changes in the heliosphere to determine the effects of acceleration at the solar wind termination shock and modulation in the heliosheath beyond that. In this paper we show that these effects have important consequences for the interpretation of secondary to primary ratios of cosmic rays at energies below 1 GeV, i.e. in the region where they are strongly modulate